A multi-material printing apparatus and method of making a gradient composite

Abstract

The application is suitable for the field of 3D printing and composite material technology, and provides a multi-material printing device and a gradient composite material preparation method.The multi-material printing device comprises a mixing structure and a printing structure.The mixing structure comprises a material cylinder and a feeding member.The material cylinder is provided with one discharge port and at least two feeding ports, and each feeding port is connected with the feeding member.The feeding member is used for conveying multiple raw materials or auxiliary materials, and when the conveying proportion of a first raw material among the multiple raw materials continuously decreases, the conveying proportion of a second raw material is controlled to continuously increase at an equal proportion.The material cylinder is provided with a stirring member.The ceramic green body with continuously gradient change of multi-material components is directly prepared by the layer-by-layer stacking method, and has the advantages of strong ceramic component and structure design and flexible controllability, and can meet the performance and functional requirements of specific parts of the composite material in actual application.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing and composite material technology, and particularly relates to a multi-material printing device and a method for preparing gradient composite materials. Background Technology

[0002] In modern engineering, the ever-growing demand for high-performance, multifunctional materials has prompted materials scientists to continuously seek new preparation methods to develop new materials that can meet performance or functional requirements in complex environments. Traditional single-component materials exhibit limitations in certain applications because they cannot simultaneously meet multiple performance requirements such as strength, toughness, lightweight, conductivity, and corrosion resistance. Against this backdrop, researchers have begun to focus on multifunctional gradient materials—materials that can exhibit different properties or functions in different regions. The unique properties of these materials make them increasingly important for applications in fields such as advanced manufacturing, aerospace, and healthcare.

[0003] Among graded materials, metal / ceramic is one of the most important. Metals are known for their excellent ductility and toughness, while ceramics possess high stiffness, strength, hardness, high temperature resistance, and corrosion resistance. Combining the two endows composite materials with superior overall performance. However, the mismatch in thermal expansion coefficients between metals and ceramics leads to significant internal stress at the interface. Homogeneous metal-ceramic composites cannot meet the requirement that material properties change with location, failing to utilize the best materials effectively. Furthermore, metal-ceramic composites are difficult to process; homogeneous composites not only waste materials but also increase processing costs. Introducing graded components into composite materials not only preserves the performance improvements brought about by the composite material but also allows for the full utilization of the superior properties of the individual components according to specific needs, thereby improving the overall performance.

[0004] However, preparing gradient composite materials with continuous transitions between multiple components is no easy task. Traditional preparation processes for gradient materials, such as powder metallurgy, centrifugal casting, and vapor deposition, are mostly limited, making it difficult to achieve continuous changes in sample composition and / or structure, and even more difficult to achieve free design and efficient preparation of shape and structure.

[0005] Currently, an emerging method is to prepare multi-component gradient materials through 3D printing. Direct ink writing (DIW) is a widely used 3D printing technology. It can precisely control the material distribution and control the material composition by setting multiple feed channels, achieving gradient changes in the printed material composition through active and passive mixing. However, the slurry suitable for DIW printing has high viscosity, high storage modulus and shear modulus, and must also exhibit shear thinning characteristics to ensure that the slurry can be extruded from a small-aperture TT needle under certain pressure and stably formed after extrusion. Due to the high viscosity of the slurry, it is difficult to uniformly mix multi-component ceramic slurries using static mixing methods, while dynamic stirring inevitably leads to shear thinning of the slurry, a decrease in storage modulus and shear modulus, with the decrease in viscosity and modulus becoming more significant with prolonged stirring time. During long printing processes, problems such as printed layer collapse and failure to form the printed part may occur. Furthermore, in multi-component material printing, there is often a significant amount of material retention in the barrel and feed tube, making it difficult to achieve component gradient changes more quickly. Another challenge lies in the continuous gradient control of multiple materials. Since different components or proportions of the slurry have different physicochemical properties, how to ensure the compatibility and consistency of multi-component slurries during the printing process, so as to achieve precise control and gradual transition of slurry composition, is also an urgent problem to be solved. Summary of the Invention

[0006] The first objective of this invention is to provide a multi-material printing apparatus that aims to solve at least one of the problems mentioned in the background art.

[0007] The present invention is implemented as follows: a multi-material printing device, the multi-material printing device including a mixing structure and a printing structure;

[0008] The mixing structure includes a material cylinder and a feeding component. The material cylinder is provided with a discharge port and at least two inlets, and each of the inlets is connected to the feeding component.

[0009] The feeding component is used to transport multiple raw materials or auxiliary materials, and to control the transport ratio of the second raw material to increase proportionally and continuously when the transport ratio of the first raw material among the multiple raw materials decreases continuously.

[0010] The material cylinder is equipped with a stirring element, which can uniformly mix various raw materials and auxiliary materials fed into the material cylinder to obtain a mixed material;

[0011] The printing structure is located at the discharge port, and the printing structure is used to control the mixed material to be printed layer by layer through the discharge port.

[0012] Furthermore, the feeding component includes an injection pump connected to the feed inlet, and the injection pump is connected to a controller, which controls the operation of the injection pump.

[0013] Furthermore, the stirring component includes a stirring paddle, a motor is mounted on the material cylinder via a motor bracket, the output end of the motor is connected to a coupling, the coupling is connected to the stirring paddle via a stainless steel rotating shaft, and the stirring paddle is located inside the material cylinder; a sealing ring is provided at the connection between the motor bracket and the material cylinder.

[0014] Furthermore, the impeller includes an impeller shaft, two or more sets of first pairs of blades and second pairs of blades alternately arranged on the impeller shaft, and any adjacent first pairs of blades and second pairs of blades have a phase difference relative to the impeller shaft; the first pairs of blades and second pairs of blades have the same structure.

[0015] Furthermore, the printing structure includes at least a connector and a needle, the connector being detachably connected to the discharge port, and the needle being connected in the connector and communicating with the discharge port.

[0016] The multi-material printing device given in the above embodiments can realize the preparation of multi-material composition gradient samples. By actively adjusting the composition ratio of the injected material through the injection pump, the continuous transition and precise control of the material composition are achieved.

[0017] By using a motor-driven custom-designed stirring paddle, online active and uniform mixing of multiple materials was achieved. Thickener was supplied via an injection pump to balance the shear thinning that occurred during mixing, ensuring stable printing slurry viscosity and improving printing success rate.

[0018] The geometry and shape of the barrel and agitator have been optimized, reducing the volume of slurry remaining in the barrel and feed pipe, enabling faster composition gradient changes. In addition, the barrel is easy to disassemble and clean, saving printing materials and improving printing efficiency.

[0019] It allows for the free construction of various configurations, greatly improving product diversity and meeting personalized design needs.

[0020] A second objective of this invention is to provide a method for preparing gradient composite materials, the method using the multi-material printing apparatus described above, the method comprising:

[0021] The process involves preparing a variety of raw materials and auxiliary materials with particle size and viscosity that meet preset specifications. Among these, the raw materials include at least a first ceramic slurry and a second ceramic slurry. The first and second ceramic slurries contain ceramic powder, dispersant, and deionized water. The auxiliary material is a thickener aqueous solution used for viscosity control.

[0022] Build a print model based on the artwork to be printed and generate print driver files;

[0023] Based on the printing driver file, the delivery ratio of the various raw materials and auxiliary materials is controlled to achieve a continuous gradient change in material composition, and the raw materials and auxiliary materials are mixed during delivery to obtain a mixed material;

[0024] Based on the printing model, the mixed materials are printed layer by layer to obtain a shaped ceramic green body with a composition gradient.

[0025] The composition gradient ceramic green body is degreased and sintered to obtain a composition gradient ceramic framework;

[0026] Liquid metal is infiltrated into a composition-gradient ceramic framework under vacuum-gas pressure conditions to obtain a composition-gradient metal-ceramic composite material.

[0027] Furthermore, the layer-by-layer printing adopts a paste extrusion direct writing molding method, with a printing accuracy in the range of 0.05 to 0.2 mm. The main printing parameters are: layer height 150 to 500 μm, and printing speed 5 to 20 mm / s.

[0028] Furthermore, the thickener is one or more of polyethylene glycol, hydroxymethyl cellulose, sodium alginate, chitosan, and polyvinyl alcohol;

[0029] The ceramic powder in the first or second ceramic slurry is one or more of alumina, zirconium oxide, mullite, silicon carbide, boron carbide, titanium carbide, and silicon nitride, and the diameter of the ceramic powder is 100 nm to 30 μm.

[0030] The dispersant is one or more of sodium polymethacrylate, sodium carboxymethyl cellulose, ammonium citrate, ammonium acrylate, Pluronic acid, and oleic acid, and the solvent is deionized water;

[0031] The delivery ratio of the first ceramic slurry and the second ceramic slurry transitions uniformly from 1:0 to 0:1 over time; and the viscosity of the mixed material is adjusted by injecting a thickener, with a delivery speed of 0.5 to 5 ml / h.

[0032] Furthermore, in the step of debinding and sintering the composition gradient ceramic green body to obtain a composition gradient ceramic framework, the debinding and sintering process is as follows:

[0033] Heat to 200℃ at a rate of 5℃ / min and hold for 10min;

[0034] Heat to 600℃ at a rate of 2℃ / min and hold for 1 hour to complete degreasing;

[0035] Then heat to 1200-2000℃ at 5℃ / min and hold for 1 hour;

[0036] Finally, the temperature was cooled to room temperature at 5℃ / min to complete the sintering.

[0037] For ceramic materials that are not susceptible to oxidation at high temperatures, degreasing and sintering are carried out in air; for ceramic materials that are susceptible to oxidation at high temperatures, degreasing and sintering are carried out under vacuum or argon conditions.

[0038] Furthermore, in the step of infiltrating liquid metal into a composition-gradient ceramic framework under vacuum-gas pressure conditions to obtain a composition-gradient metal-ceramic composite material, the infiltration and injection process is as follows:

[0039] The metal block is placed on top of the composition gradient ceramic skeleton and together they are placed in an alumina crucible. The alumina crucible is then placed in a pressure infiltration furnace.

[0040] The pressure impregnation furnace is evacuated to below 10 Pa, and then heated at a rate of 5 °C / min to 50–200 °C above the metal melting point.

[0041] High-purity argon gas with a purity of 99.999% is introduced to bring the pressure inside the pressure impregnation furnace to 2-5 MPa;

[0042] Cool to below the metal's melting point at a rate of 5°C / min, then depressurize and cool to room temperature with the furnace.

[0043] The gradient composite material preparation method provided by the embodiments of the present invention is simple, flexible, economical and efficient, with a wide range of selectable ceramic and metal materials, high designability of composition and structure, high degree of freedom, and universality. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a multi-material printing device provided in an embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of the structure of the stirring paddle in one embodiment;

[0046] Figure 3 This is a physical image of a B4C / Al2O3 sample with a continuous transition in composition printed by a multi-material printing device in one embodiment.

[0047] Figure 4 This is a schematic flowchart of a gradient composite material preparation method provided in an embodiment of the present invention;

[0048] Figure 5An example of a gradient composite material obtained in one embodiment, wherein (a) is a physical image of a layered gradient SiC / Al2O3 ceramic skeleton, (b) is the microstructure of five regions (I-V) of the green body, (c) is a macroscopic image of the layered Al-SiC / Al2O3 gradient composite material, and (d) is the microstructure of five regions (I-V) of the gradient composite material.

[0049] Figure 6 The three-point bending stress-strain curves of region I-V of the Al-SiC / Al2O3 gradient composite material obtained in one embodiment are shown when loaded along the parallel lamellar direction.

[0050] Figure 7 Al-B4C / Al2O3 gradient composite material obtained in another embodiment, wherein (a) is a macroscopic image and (b) is a scanning electron microscope image of the microstructure of the five regions (I-V) of the gradient composite material;

[0051] Figure 8 Three-point bending stress-strain curves of an Al-B4C / Al2O3 gradient composite material in regions I-V without pre-fabricated notches when loaded along the direction perpendicular to the lamellar direction in another embodiment.

[0052] Figure 9 The three-point bending stress-displacement curve of the Al-B4C / Al2O3 gradient composite material I-V region obtained in another embodiment when loaded along the direction perpendicular to the lamellar layer is shown.

[0053] In the diagram: 1-Motor; 2-Coupling; 3-Stainless steel shaft; 4-Motor bracket; 5-Barrel; 6-Sealing ring; 7-First injection pump; 8-Second injection pump; 9-Other injection pumps; 10-Agitator; 101-First pair of blades; 102-Second pair of blades; 103-Agitator shaft; 11-Metal Luer connector; 12-TT needle; 13-Controller; 14-Barrel storage tank; 15-Third injection pump. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0055] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0056] This invention provides a multi-material printing device, which is a slurry extrusion direct-write 3D printer driven by an injection pump. It can manufacture parts or products layer by layer according to the designed composition and pattern, and has high precision and multi-material printing capabilities. It is equipped with a small, easily disassembled, and easy-to-clean material cylinder 5. The material cylinder 5 has multiple feed ports connected to multiple injection pumps. The injection pumps are responsible for introducing ceramic slurries of different components into the material cylinder 5, while precisely controlling the feed amount. A motor-driven custom stirring paddle 10 is installed inside the material cylinder 5 to uniformly stir the different ceramic slurry components injected into the material cylinder 5. One of the injection pumps injects a thickener to balance the significant shear thinning of the ceramic slurry after continuous stirring, thereby achieving viscosity control and ensuring printing stability.

[0057] Figure 1 This is a schematic diagram of a multi-material printing device provided in an embodiment of the present invention, wherein the multi-material printing device includes a mixing structure and a printing structure;

[0058] The mixing structure includes a material cylinder 5 and a feeding component. The material cylinder 5 is provided with a discharge port and at least two inlets, and each of the inlets is connected to the feeding component.

[0059] The feeding component is used to transport multiple raw materials or auxiliary materials, and to control the transport ratio of the second raw material to increase proportionally and continuously when the transport ratio of the first raw material among the multiple raw materials decreases continuously.

[0060] The material cylinder 5 is equipped with a stirring element, which can uniformly mix various raw materials and auxiliary materials conveyed into the material cylinder 5 to obtain a mixed material;

[0061] The printing structure is located at the discharge port and is used to control the mixed material to be printed layer by layer through the discharge port; the printing structure utilizes direct ink writing (DIW) 3D printing technology, abbreviated as DIW printing technology.

[0062] In one example of this embodiment, the multiple materials can be one or more of SiC / Al2O3, B4C / Al2O3, or alumina, zirconium oxide, mullite, silicon carbide, boron carbide, titanium carbide, silicon nitride, etc., or other ceramic composite materials. The composition gradient metal-ceramic composite material can be Al-SiC / Al2O3, Al-B4C / Al2O3, or other multi-component ceramic and metal (such as various Al alloys, Cu or Cu alloys, etc.). Due to space limitations, they will not be listed exhaustively here.

[0063] The thickener is one or more of polyethylene glycol, hydroxymethyl cellulose, sodium alginate, chitosan, and polyvinyl alcohol. The thickener is supplied to the barrel by an injection pump according to a set program to balance the significant shear thinning of raw materials and auxiliary materials during continuous stirring. The specific components and injection amount of the thickener can be flexibly adjusted according to requirements.

[0064] In one example of this embodiment, the feeding component includes an injection pump connected to the feed port. The injection pump is connected to a controller, which controls the operation of the injection pump. The injection pump can be connected to a storage cylinder 14 for temporarily storing raw materials or auxiliary materials.

[0065] In this example, there are 2 to 4 feed ports; taking 2 as an example, one of them is set as the feed port for auxiliary materials, which is connected to the third injection pump 15 for the injection or delivery of thickener; the other is connected to a multi-way valve, such as a three-way valve or a four-way valve, which can be connected to the first injection pump 7, the second injection pump 8, and other injection pumps 9 for the injection or delivery of the first raw material, the second raw material, and other raw materials; of course, other injection pumps 9 can also be connected to other feed ports, which will not be described in detail here.

[0066] In one example of this embodiment, the stirring component includes a stirring paddle 10, and a motor 1 is mounted on the material cylinder 5 via a motor bracket 4. The output end of the motor 1 is connected to a coupling 2, and the coupling 2 can be connected to the stirring paddle 10 via a stainless steel rotating shaft 3. The stirring paddle 10 is located inside the material cylinder 5. A sealing ring 6 is provided at the connection between the motor bracket 4 and the material cylinder 5, and the sealing ring 6 serves a sealing function.

[0067] In one example of this embodiment, the speed of motor 1 is infinitely adjustable within the range of 0 to 1500 rpm, which can fully stir various raw materials and auxiliary materials in the material cylinder 5 to ensure that the components are uniform.

[0068] In one example of this embodiment, the barrel 5 is made of nylon material, with an inner diameter of 9-10 mm and a volume of 3-5 ml; the barrel is provided with 2-4 feed ports, with an inner diameter of 2-6 mm; a stirring paddle 10 is installed inside the barrel 5, the stirring paddle 10 is an innovatively designed structure printed using fused deposition modeling (FDM) machine, the rod length of the stirring paddle 10 is 55 mm, and the maximum profile diameter is 8.5 mm.

[0069] In one example of this embodiment, the stirring paddle 10 includes a stirring shaft 103, two or more sets of first pairs of blades 101 and second pairs of blades 102 alternately arranged on the stirring shaft 103, and any adjacent first pairs of blades 101 and second pairs of blades 102 have a phase difference relative to the stirring shaft 103; the first pairs of blades 101 and second pairs of blades 102 have the same structure.

[0070] like Figure 2 As shown, in the first pair of blades 101 and the second pair of blades 102, each pair consists of two symmetrically distributed blades, and the next pair consists of two blades with opposite inclination directions and perpendicularly intersecting each other, i.e., a phase difference of 180°, and so on, arranged alternately; of course, the phase difference can also be other, such as 90° or 120°. The upper end of the stirring blade 10 is fixed to the stainless steel rotating shaft 3 below the coupling 2 by screws, and the stainless steel rotating shaft 3 is connected to the motor 1 through the coupling 2; the gap between the stirring blade 10 and the inner wall of the barrel 5 is 0.5mm, and the gap between the stirring blade 10 and the bottom of the barrel 5 is 1-2mm.

[0071] In this example, taking the printing of B4C / Al2O3 as an example: the rotation of blades with opposite tilting directions causes the mixed material (or mixed slurry) to tumble up and down, which is different from the traditional screw-type unidirectional pushing mixing method. This bidirectional stirring has a better mixing effect; the upper end of the stirring paddle 10 is fixed to the stainless steel rotating shaft 3 below the coupling 2 by screws. The stainless steel rotating shaft 3 is connected to the rotating shaft or output end of the motor 1 through the coupling 2; the gap between the stirring paddle 10 and the inner wall of the barrel 5 is 0.5mm, and the gap between the stirring paddle 10 and the bottom of the barrel 5 is 1-2mm. The printing process begins by fully filling the cylinder 5 with ceramic slurry A (the first raw material) using the first injection pump 7. Then, the second injection pump 8 is activated, simultaneously introducing ceramic slurry A and ceramic slurry B (the first and second raw materials, respectively). (A three-way or four-way connector can be used to increase the material flow channels, or other injection pumps 9 can be connected to allow for the input of more component slurries.) The injection pumps control the input ratio of ceramic components according to the program set in the controller 13, with the ratio of ceramic slurry A to ceramic slurry B gradually transitioning from 1:0 to 0:1, ensuring that the printed ceramic green body gradually transitions from 100% ceramic slurry A to nearly 100% ceramic slurry B. Simultaneously, a thickener is continuously injected through the third injection pump 15 to maintain the stability of the mixed slurry viscosity during printing. As printing progresses, the content of ceramic slurry B increases, and the components are uniformly mixed under the action of the stirring paddle 10 driven by the motor 1. (The printed product is shown in the image.) Figure 3 ( Figure 3 (Taking B4C / Al2O3 as an example).

[0072] In one example of this embodiment, such as Figure 2 As shown, the blades are conical, and the conical shape of the blades near the inner wall of the barrel bends towards the axial direction of the rod.

[0073] In one example of this embodiment, the printing structure includes at least a connector and a needle, the connector being detachably connected to the discharge port, and the needle being connected in the connector and communicating with the discharge port.

[0074] In one example of this embodiment, the connector can be a metal Luer connector 11, and the needle can be a TT needle 12.

[0075] The upper end of the barrel 5 is connected to the motor bracket 4 by a thread and is sealed by the compression sealing ring 6; the lower end of the barrel 5 is connected to the metal Luer connector 11 by a thread, and the metal Luer connector 11 is connected to the TT needle 12 by a thread, both of which can be easily disassembled.

[0076] In one example of this embodiment, the printing structure further includes a host computer (which can be a microcomputer, desktop computer, or cloud server, etc.). The host computer uses 3D modeling software to construct a layered printing model. Then, direct ink writing (DIW) 3D printing technology is used to form the ceramic slurry into a ceramic green body. The printing parameters are set as follows: layer height 150–500 μm, printing speed 5–20 mm / s. During printing, a TT needle with a size of 20–30 G (needle inner diameter 0.16–0.6 mm) is selected. A constant temperature environment is activated, and a fan is used for ventilation to promote green body drying. A third injection pump 15 injects a thickener aqueous solution to adjust the viscosity of the ceramic slurry at an injection rate of 0.5–5 ml / h. During printing, the speed of motor 1 is infinitely adjustable within the range of 0–1500 rpm, which can fully stir the ceramic slurry in the barrel 5 to ensure uniform composition.

[0077] In the above embodiments, a multi-material printing device can prepare samples with gradient compositions of multiple materials. By actively controlling the component ratio of the injected materials through an injection pump, continuous transition and precise control of material components are achieved. A customized stirring paddle 10 driven by a motor 1 enables online active and uniform mixing of multiple materials. Thickener is supplied through the injection pump, balancing the shear thinning that occurs during mixing, ensuring stable printing slurry viscosity, and improving printing success rate. The optimized geometry and shape of the barrel 5 and stirring paddle 10 reduce the slurry retention volume in the barrel 5 and delivery pipe, achieving faster composition gradient changes. Furthermore, the barrel 5 is easy to disassemble and clean, saving printing material and improving printing efficiency. It can freely construct various configurations, greatly improving product diversity and meeting personalized design needs.

[0078] like Figure 4 As shown, in another embodiment, a method for preparing a gradient composite material, the method using the multi-material printing apparatus described above, the method comprising:

[0079] The process involves preparing a variety of raw materials and auxiliary materials with particle size and viscosity that meet preset specifications. Among these, the raw materials include at least a first ceramic slurry and a second ceramic slurry. The first and second ceramic slurries contain ceramic powder, dispersant, and deionized water. The auxiliary material is a thickener aqueous solution used for viscosity control.

[0080] Build a print model based on the artwork to be printed and generate print driver files;

[0081] Based on the printing driver file, the delivery ratio of the various raw materials and auxiliary materials is controlled to achieve a continuous gradient change in material composition, and the raw materials and auxiliary materials are mixed during delivery to obtain a mixed material;

[0082] Based on the printing model, the mixed multi-component materials (i.e., mixed materials) are printed layer by layer to obtain a shaped composition gradient ceramic green body.

[0083] The composition gradient ceramic green body is degreased and sintered to obtain a composition gradient ceramic framework;

[0084] Liquid metal is infiltrated into a composition-gradient ceramic framework under vacuum-gas pressure conditions to obtain a composition-gradient metal-ceramic composite material.

[0085] In one example of this embodiment, the layer-by-layer printing is performed using a slurry extrusion direct writing molding method; that is, direct ink writing (DIW) 3D printing technology, or DIW printing technology for short. The printing accuracy is in the range of 0.05 to 0.2 mm, and the main printing parameters are: layer height 150 to 500 μm, and printing speed 5 to 20 mm / s.

[0086] In one example of this embodiment, the thickener is one or more of polyethylene glycol, hydroxymethyl cellulose, sodium alginate, chitosan, and polyvinyl alcohol;

[0087] The ceramic material in the first or second ceramic slurry is one or more of alumina, zirconium oxide, mullite, silicon carbide, boron carbide, titanium carbide, and silicon nitride.

[0088] The dispersant is one or more of sodium polymethacrylate, sodium carboxymethyl cellulose, ammonium citrate, ammonium acrylate, Pluronic acid, and oleic acid, and the solvent is deionized water;

[0089] The delivery ratio of the first ceramic slurry and the second ceramic slurry transitions uniformly from 1:0 to 0:1 over time; and the viscosity of the mixed material is adjusted by injecting a thickener, with a delivery speed of 0.5 to 5 ml / h.

[0090] In this example, the first ceramic slurry is ceramic slurry A, and the second ceramic slurry is ceramic slurry B. Ceramic powder A and ceramic powder B are added to a dispersant and deionized water in a certain proportion, and then ball-milled to obtain uniformly dispersed ceramic slurry A and ceramic slurry B. At the same time, a thickener aqueous solution for viscosity control is prepared.

[0091] Among them, the components of ceramic powder A are one or more of alumina, zirconium oxide, mullite, silicon carbide, boron carbide, titanium carbide, silicon nitride, etc., which can be flexibly selected; the diameter of ceramic powder A is 100nm~30μm; for example, Al2O3 ceramic powder, or ceramic powder A is SiC ceramic powder; while ceramic powder B is different or exactly the opposite.

[0092] In this example, ceramic powder A and ceramic powder B are added to a dispersant and deionized water in a certain proportion, respectively, and then ball-milled to obtain uniformly dispersed ceramic slurry A and ceramic slurry B. Simultaneously, a thickener aqueous solution for viscosity control is prepared. The ceramic content in ceramic slurry A and ceramic slurry B is 35–55 vol.%, and the dispersant content is 1–5% of the ceramic powder mass; the thickener content in the thickener aqueous solution is 2–5 wt.%; the ball milling speed is 800–1500 rpm, each ball milling time is 10 min, and the ball milling is repeated 4–8 times.

[0093] In one example of this embodiment, in the step of debinding and sintering the composition gradient ceramic green body to obtain a composition gradient ceramic skeleton, the debinding and sintering process is as follows:

[0094] Heat to 200℃ at a rate of 5℃ / min and hold for 10min;

[0095] Heat to 600℃ at a rate of 2℃ / min and hold for 1 hour to complete degreasing;

[0096] Then heat to 1200-2000℃ at 5℃ / min and hold for 1 hour;

[0097] Finally, the temperature was cooled to room temperature at 5℃ / min to complete the sintering.

[0098] For ceramic materials that are not susceptible to oxidation at high temperatures, degreasing and sintering are carried out in air; for ceramic materials that are susceptible to oxidation at high temperatures, degreasing and sintering are carried out under vacuum or argon conditions.

[0099] In the step of infiltrating liquid metal into a composition-gradient ceramic framework under vacuum-gas pressure conditions to obtain a composition-gradient metal-ceramic composite material, the infiltration and injection process is as follows:

[0100] The metal block is placed on top of the composition gradient ceramic skeleton and together they are placed in an alumina crucible. The alumina crucible is then placed in a pressure infiltration furnace.

[0101] The pressure impregnation furnace is evacuated to below 10 Pa, and then heated at a rate of 5 °C / min to 50–200 °C above the metal melting point.

[0102] High-purity argon gas with a purity of 99.999% is introduced to bring the pressure inside the pressure impregnation furnace to 2-5 MPa;

[0103] The metal was cooled at a rate of 5°C / min to below its melting point, then depressurized and cooled to room temperature in the furnace to obtain the gradient composite material.

[0104] In one example of this embodiment, microstructure analysis and mechanical property testing can be performed when fabricating green bodies (composition gradient ceramic green bodies) and gradient composite materials.

[0105] In one example of this embodiment, the preparation method of a layered (1 mm interlayer spacing) compositional gradient metal-ceramic (Al-SiC / Al2O3) composite material includes the following steps:

[0106] Step 1: Add Al2O3 ceramic powder (D 50 =3μm, purity 99.7%), dispersant (Prönnicke, 3wt.% of ceramic powder mass) and deionized water were mixed to prepare an Al2O3 ceramic slurry with a solid content of 40 vol.%; SiC ceramic powder (D 50 =5μm, purity 99.7%), dispersant (sodium carboxymethyl cellulose, accounting for 3wt.% of the ceramic powder mass) and deionized water were mixed to prepare a SiC ceramic slurry with a solid content of 40 vol.%; after ball milling (ball milling speed of 800 rpm, ball milling time of 10 min each time, ball milling 5 times), the desired Al2O3 and SiC ceramic slurry was obtained; and then, using magnetic stirring, hydroxymethyl cellulose (CMC) and deionized water were mixed to prepare a thickener with a content of 2 wt.% at a heating temperature of 40℃ and a stirring time of 30 min;

[0107] Step 2: The obtained ceramic slurry is shaped using a multi-material printing device to obtain a SiC-Al2O3 green body. Specifically, a printing model is established, and a printing driver file is generated based on the printing model. The processing path is then generated using slicing software based on the printing driver file or directly based on the printing model. The interlayer spacing is 1 mm, the interlayer height is 200 μm, the printing height is 20 mm, and the printing speed is 7 mm / s. During printing, a ceramic slurry A (i.e., SiC ceramic slurry) is first filled into the barrel 5 through the first injection pump 7, and a 25G (needle inner diameter of 0.25 mm) TT needle 12 is installed. Then, the first injection pump 7 and the second injection pump 8 are turned on to simultaneously introduce ceramic slurry A (SiC ceramic slurry) and ceramic slurry B (Al2O3 ceramic slurry). The ratio of ceramic slurry A to ceramic slurry B introduced gradually changes from 1:0 to 0:1 over time. Simultaneously, a carboxymethyl cellulose (CMC) thickener solution is continuously injected into the barrel 5 via the third injection pump 15 at a rate of 1 ml / h to maintain the stability of the mixed slurry viscosity. During printing, the motor 1 speed is set to 800 rpm. To accelerate the drying process, an additional fan needs to be turned on to increase the airflow around the printed sample.

[0108] Step 3: The printed SiC-Al2O3 green body is degreased and sintered in air to obtain a layered SiC-Al2O3 ceramic framework. Specifically, the temperature is increased to 200℃ at 5℃ / min and held for 10 min, then increased to 600℃ at 2℃ / min and held for 1 h to complete the degreasing; then it is heated to 1200℃ at 5℃ / min and held for 1 h, and finally cooled to room temperature at 5℃ / min to complete the sintering.

[0109] Step 4: Liquid metallic Al is infiltrated into a layered SiC-Al2O3 ceramic framework under vacuum-gas pressure conditions to obtain a layered compositional gradient metal-ceramic composite material, namely, an Al-SiC / Al2O3 gradient composite material. Specifically, before the experiment begins, a block of pure aluminum (a block of metallic Al) is placed on top of the ceramic framework and together they are placed in an alumina crucible, which is then placed in a pressure infiltration furnace. The pressure infiltration furnace is evacuated to below 10 Pa, and then heated to 850 °C at 5 °C / min. High-purity argon gas with a purity of 99.999% is introduced to bring the pressure inside the pressure infiltration furnace to the preset pressure of 2 MPa. Finally, it is cooled to below the melting point of the metal at a rate of 5 °C / min, the pressure is released, and the furnace is cooled to room temperature.

[0110] The physical specimen of the SiC-Al2O3 ceramic framework obtained in this embodiment is shown below. Figure 5 (a) The ceramic framework is divided into five regions, namely Region I to Region V; the corresponding scanning electron microscope images of the microstructure are as follows: Figure 5 As shown in (b); the actual product of the prepared Al-SiC / Al2O3 composite material is shown in [image / image]. Figure 5 As shown in (c); the microstructures of the five regions (Ⅰ-Ⅴ) are as follows Figure 5 As shown in (d), from Region I to Region V, the number of SiC particles gradually decreases, while the number of Al2O3 particles gradually increases. Figure 6 The three-point bending stress-strain curves of the five (I-V) regions of the gradient composite material under load along the parallel lamellar direction show obvious gradient variation characteristics.

[0111] In one embodiment, taking the preparation of a layered (interlayer spacing of 0.8 mm) compositional gradient metal-ceramic (Al-B4C / Al2O3) composite material as an example, the preparation method includes the following steps:

[0112] Al2O3 ceramic powder (D 50 =3μm, purity 99.7%), dispersant (sodium polymethacrylate, 3wt.% of Al2O3 ceramic powder) and deionized water were mixed to prepare an Al2O3 ceramic slurry with a solid content of 40 vol.%; B4C ceramic powder (D 50 A B4C ceramic slurry with a solid content of 40 vol% was prepared by mixing a 5 μm particle size (96% purity), a dispersant (Planic, 3 wt.% of the B4C ceramic powder), and deionized water. The slurry was ball-milled (1000 rpm, 10 min per milling cycle, 5 times) to obtain the desired slurry. A multi-material printing device was used, and slicing software was used to generate the processing path. The interlayer spacing was 0.8 mm, and the remaining printing parameters were the same as in the previous embodiment. Under an argon atmosphere, the temperature was increased to 200°C at 5°C / min and held for 10 min, then increased to 600°C at 2°C / min and held for 1 h to complete degreasing. Then, the temperature was increased to 1500°C at 5°C / min and held for 1 h, and finally cooled to room temperature at 5°C / min to complete sintering, obtaining a B4C / Al2O3 ceramic framework. The infiltration parameters were the same as in the previous embodiment.

[0113] In this embodiment, the actual B4C / Al2O3 ceramic framework is as follows: Figure 3 As shown, the Al-B4C / Al2O3 composite material is as follows: Figure 7 As shown in (a), the composite material is divided into five regions, namely Region I to Region V, according to the different compositions at different heights; Figure 7 (b) is a scanning electron microscope image of the microstructure of five regions (Ⅰ-Ⅴ) of the Al-B4C / Al2O3 composite material; from Region Ⅰ to Region VA, the number of B4C particles gradually decreases and the number of Al2O3 particles gradually increases. Figure 8 Three-point bending stress-strain curves of a gradient composite material sample without pre-fabricated notches in regions I-V; Figure 9The three-point bending stress-displacement curves of the gradient composite material sample with pre-fabricated notches in region I-V under load along the direction perpendicular to the lamellar layers show a clear gradient change in mechanical properties.

[0114] Therefore, the multi-material printing apparatus provided in the foregoing embodiments of this application can prepare samples with gradient compositions of multiple materials. By actively controlling the component ratio of the injected materials through an injection pump, continuous transition and precise control of material components are achieved. A customized stirring paddle driven by a motor enables online active and uniform mixing of multiple materials, and a thickener supplied by the injection pump balances the shear thinning that occurs during mixing, ensuring stable printing slurry viscosity and improving printing success rate. The optimized geometry and shape of the barrel and stirring paddle reduce the slurry retention volume in the barrel and delivery pipe, achieving faster composition gradient changes. Furthermore, the barrel is easy to disassemble and clean, saving printing material and improving printing efficiency. It allows for the free construction of various configurations, greatly improving product diversity and meeting personalized design needs.

[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-material printing apparatus, characterized in that, The multi-material printing device includes a mixing structure and a printing structure; The mixing structure includes a barrel and a feeding component. The barrel has one outlet and at least two inlets, each of which is connected to the feeding component. The feeding component includes an injection pump connected to each inlet. The injection pump is connected to a controller, which controls the operation of the injection pump. One of the injection pumps injects a thickener aqueous solution to balance the significant shear thinning of the ceramic slurry after continuous stirring, thereby achieving viscosity control. The barrel is a small-volume barrel with a capacity of 3-5 ml. The feeding component is used to transport multiple raw materials or auxiliary materials, and to control the transport ratio of the second raw material to increase proportionally and continuously when the transport ratio of the first raw material among the multiple raw materials decreases continuously; the auxiliary material is a thickener aqueous solution; A stirring element is rotatably installed inside the material cylinder. The stirring element can uniformly mix various raw materials and auxiliary materials fed into the material cylinder to obtain a mixed material. The stirring element includes a motor and a stirring paddle. The motor is mounted on the material cylinder via a motor bracket. The output end of the motor is connected to a coupling. The coupling is connected to the stirring paddle via a stainless steel rotating shaft. The stirring paddle is located inside the material cylinder. The gap between the stirring paddle and the inner wall of the material cylinder is 0.5 mm, and the gap between the stirring paddle and the bottom of the material cylinder is 1-2 mm. The speed of the motor is infinitely adjustable within the range of 0-1500 rpm, which can fully mix various raw materials and auxiliary materials in the material cylinder. The printing structure is located at the discharge port, and the printing structure is used to control the mixed material to be printed layer by layer through the discharge port.

2. The multi-material printing apparatus according to claim 1, characterized in that, A sealing ring is provided at the connection between the motor bracket and the material cylinder.

3. The multi-material printing apparatus according to claim 2, characterized in that, The stirring paddle includes a stirring shaft and two or more sets of first pairs of blades and second pairs of blades alternately arranged on the stirring shaft. Any adjacent first pairs of blades and second pairs of blades have a phase difference relative to the stirring shaft. The first pairs of blades and second pairs of blades have the same structure.

4. The multi-material printing apparatus according to claim 1, characterized in that, The printing structure includes at least a connector and a needle, the connector being detachably connected to the discharge port, and the needle being connected to the connector and communicating with the discharge port.

5. A method for preparing gradient composite materials, characterized in that, The method is used in the multi-material printing apparatus as described in any one of claims 1-4, the method comprising: The process involves preparing a variety of raw materials and auxiliary materials with particle size and viscosity that meet preset specifications. Among these, the raw materials include at least a first ceramic slurry and a second ceramic slurry. The first and second ceramic slurries contain ceramic powder, dispersant, and deionized water. The auxiliary material is a thickener aqueous solution. Build a print model based on the artwork to be printed and generate print driver files; Based on the printing driver file, the delivery ratio of the various raw materials and auxiliary materials is controlled to achieve a continuous gradient change in material composition. The raw materials and auxiliary materials are mixed during delivery to obtain a mixed material. The delivery ratio of the first ceramic slurry and the second ceramic slurry transitions uniformly from 1:0 to 0:1 over time, and the viscosity of the mixed material is adjusted by injecting a thickener aqueous solution. Based on the printing model, the mixed materials are printed layer by layer to obtain a shaped ceramic green body with a composition gradient. The composition gradient ceramic green body is degreased and sintered to obtain a composition gradient ceramic framework; Liquid metal is infiltrated into a composition-gradient ceramic framework under vacuum-gas pressure conditions to obtain a composition-gradient metal-ceramic composite material.

6. The method for preparing gradient composite materials according to claim 5, characterized in that, The layer-by-layer printing is performed using a paste extrusion direct writing method, with a printing accuracy in the range of 0.05~0.2 mm. The main printing parameters are: layer height 150~500 μm, printing speed 5~20 mm / s.

7. The method for preparing gradient composite materials according to claim 5, characterized in that, The thickener is one or more of polyethylene glycol, hydroxymethyl cellulose, sodium alginate, chitosan, and polyvinyl alcohol; The ceramic powder in the first or second ceramic slurry is one or more of alumina, zirconium oxide, mullite, silicon carbide, boron carbide, titanium carbide, and silicon nitride, and the diameter of the ceramic powder is 100 nm to 30 μm. The dispersant is one or more of sodium polymethacrylate, sodium carboxymethyl cellulose, ammonium citrate, ammonium acrylate, Pluronic acid, and oleic acid, and the solvent is deionized water; The delivery ratio of the first ceramic slurry and the second ceramic slurry transitions uniformly from 1:0 to 0:1 over time; and the viscosity of the mixed material is adjusted by injecting a thickener aqueous solution, with a delivery speed of 0.5~5 ml / h.

8. The method for preparing gradient composite materials according to claim 5, characterized in that, In the step of debinding and sintering the composition gradient ceramic green body to obtain a composition gradient ceramic framework, the debinding and sintering process is as follows: Increase the temperature to 200℃ at a rate of 5℃ / min and hold for 10 min; The temperature was increased to 600℃ at a rate of 2℃ / min and held for 1 hour to complete the degreasing process. Then heat to 1200~2000 ℃ at 5 ℃ / min and hold for 1 h; Finally, the temperature was cooled to room temperature at 5 °C / min to complete the sintering. For ceramic materials that are not susceptible to oxidation at high temperatures, degreasing and sintering are carried out in air; for ceramic materials that are susceptible to oxidation at high temperatures, degreasing and sintering are carried out under vacuum or argon conditions.

9. The method for preparing gradient composite materials according to claim 5, characterized in that, In the step of infiltrating liquid metal into a composition-gradient ceramic framework under vacuum-gas pressure conditions to obtain a composition-gradient metal-ceramic composite material, the infiltration and injection process is as follows: The metal block is placed on top of the composition gradient ceramic skeleton and together they are placed in an alumina crucible. The alumina crucible is then placed in a pressure infiltration furnace. The pressure impregnation furnace is evacuated to below 10 Pa, and then heated at a rate of 5 °C / min to 50-200 °C above the metal melting point. High-purity argon gas with a purity of 99.999% is introduced to bring the pressure inside the pressure infiltration furnace to 2~5 MPa; it is then cooled to below the metal melting point at a rate of 5℃ / min, the pressure is released, and the furnace is cooled to room temperature.

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